Amino Acids

Amino acids are the building blocks (monomers) of proteins. 20 different amino acids are used to synthesize proteins. The shape and other properties of each protein is dictated by the precise sequence of amino acids in it.

Each amino acid consists of an alpha carbon atom to which is attached




The Amino Acids
(For each amino acid, both the three-letter and single-letter codes are given. CLICK the NAME to see the structural formula)
AlanineAlaAhydrophobic
ArginineArgRfree amino group makes it basic and hydrophilic
AsparagineAsnNcarbohydrate can be covalently linked ("N-linked) to its -NH
Aspartic acidAspDfree carboxyl group makes it acidic and hydrophilic
CysteineCysCoxidation of their sulfhydryl (-SH) groups link 2 Cys (S-S)
Glutamic acidGlyEfree carboxyl group makes it acidic and hydrophilic
GlutamineGlnQmoderately hydrophilic
GlycineGlyGso small it is amphiphilic (can exist in any surroundings)
HistidineHisHbasic and hydrophilic
IsoleucineIleIhydrophobic
LeucineLeuLhydrophobic
LysineLysKstrongly basic and hydrophilic
MethionineMetMhydrophobic
PhenylalaninePheFvery hydrophobic
ProlineProPcauses kinks in the chain
SerineSerScarbohydrate can be covalently linked ("O-linked") to its -OH
ThreonineThrTcarbohydrate can be covalently linked ("O-linked") to its -OH
TryptophanTrpWscarce in most plant proteins
TyrosineTyrY-OH group makes it moderately hydrophilic
ValineValVhydrophobic

Humans must include adequate amounts of 9 amino acids in their diet. These "essential" amino acids cannot be synthesized from other precursors. However, cysteine can partially meet the need for methionine (they both contain sulfur), and tyrosine can partially substitute for phenylalanine.

The Essential Amino Acids
Histidine
Isoleucine
Leucine
Lysine
Methionine (and/or cysteine)
Phenylalanine (and/or tyrosine)
Threonine
Tryptophan
Valine
Two of the essential amino acids, lysine and tryptophan, are poorly represented in most plant proteins. Thus strict vegetarians should take special pains to ensure that their diet contains sufficient amounts of these two amino acids.
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11 March 1996